Very popular in Ireland yet unknown in the UK, this is a Band III slot dipole with reflectors. The slot dipole is a curious concept, but think of it as a sort of ‘negative’ of a normal dipole. The rectangular slot actually represents the boundary of a hole in an infinitely large sheet of conductive material. The hole is half a wavelength long and much less than half a wavelength wide. It responds to the magnetic rather than the electric field, so has the opposite physical polarity to a normal dipole. Hence the horizontal slot seen here with the signal tapped at the centre midpoints of the top and bottom sides responds to ‘vertical’ polarisation. Since the midpoints of the sides have zero current they can be used to support the reflector arms.

This is all very impressive scientific stuff, but does this aerial work? Well, no. A glance at the radiation pattern so kindly provided by Andy Green shows that the same amount of aluminium, had it been assembled into a conventional yagi, would have performed far better. The only redeeming feature is the bandwidth, which incidentally is set by the width of the slot.